A piston reciprocating in a cylinder bore of an internal combustion engine has a plurality of ring grooves (for example, three ring grooves). For example, two compression rings (chiefly, a first ring that seals a combustion gas and a second ring that seals the combustion gas and adjusts a lubricant film) used to prevent a combustion gas from blowing through and an oil ring consisting of a plurality of components to adjust the lubricant film are fitted in these ring grooves. A connecting rod is swingably connected to the piston.
A known conventional device for installing these piston rings is made up of a cylindrical guide member whose diameter becomes greater upwardly from below and that has a concave part to receive a head of a piston at its upper end, a ring feeding mechanism that pushes up the piston rings stacked and held on the outer periphery of the guide member from below, and a robot that places the piston toward the concave part of the guide member (see Japanese Unexamined Patent Publication No. H8-90359, for example).
However, in the device disclosed by this publication, if the piston is disposed in the concave part in a slightly inclined state when the piston is transferred to and positioned in the concave part of the guide member by means of the robot, the piston rings guided by the outer circumferential surface of the guide member do not become parallel to the ring grooves of the piston, and hence there is a fear that a mistake will occur in installing the piston rings.
Therefore, disadvantageously, there is a need to perform positioning in a horizontal direction and positioning in a vertical direction with high accuracy when the piston is positioned in the concave part, and productivity is reduced if the control speed of the robot is decreased.
Another known conventional device for installing the piston rings is made up of a cylindrical guide member, a ring feeding mechanism that pushes up the piston rings stacked and held on the outer periphery of the guide member from below, an exterior inner-diameter restraining jig, and an interior inner-diameter restraining jig that is disposed coaxially with the exterior inner-diameter restraining jig and that has a concave part to receive a head of a piston at its upper end in order to guide the piston rings fed to the upper end of the guide member to the ring grooves while reducing their diameters through multiple stages (see Japanese Unexamined Patent Publication No. H11-179622, for example).
However, in the device disclosed by this publication, since positioning is performed by a manual operation or by a handling device, such as a robot, when the piston is positioned in the concave part, a positioning problem occurs as in the above conventional device. Additionally, disadvantageously, since the diameters of the piston rings are reduced through multiple stages, much time is consumed to reach the step of installing the piston rings, and productivity is reduced.
The present invention has been made in consideration of the circumstances of the conventional technique. It is therefore an object of the present invention to provide a piston-ring-installing device and method capable of improving the positioning accuracy of a piston, capable of improving productivity, and capable of reducing cost while increasing processing speed with a simple mechanical structure without employing, for example, a complex control sequence.